1. Field of the Invention
The present invention relates to an image display device and, more specifically, to an image display device that is capable of appropriately changing a direction in which a virtual image is presented to a user.
2. Description of the Related Art
In recent years, so-called head up displays that use LEDs or semiconductor laser light sources have been developed as image display devices. Head up displays are provided with an optical element called combiner. This combiner allows light that enters from outside a vehicle to pass through and displays to a user, as a virtual image, an image related to image display light that is projected. Via this combiner, the user is able to recognize the virtual image while overlapping the virtual image on a landscape the user is actually viewing.
Head up displays such as those described above have received attention as display devices for vehicles in recent years since the head up displays allow a driver to recognize a landscape outside the vehicle and image displaying various types of information almost without changing the line of sight or a focal position of the eyes. Also, technological development has been actively made for presenting an appropriate virtual image in a visual-line direction of a driver or the like.
For example, Patent document No. 1 suggests a method that allows a virtual image to be recognized even when the position of the eyes of the driver changes in the upward and downward directions by adjusting the angle of a mirror that projects an image onto a combiner. Patent document No. 2 suggests a method of adjusting the angle of a combiner and an entire image generation unit in an integral manner.
[Patent document No. 1] Japanese Unexamined Patent Publication No. 5-229366
[Patent document No. 2] Japanese Patent No. 4847627
Various limitations on a mounting position and a size are required for head up displays. For example, head up displays that are mounted in a vehicle are required to be appropriately installable according to various types of vehicles. Even after installation, head up displays are also required to be able to appropriately present a virtual image even when, for example, there is a change in the position of eyes of a driver in accordance with the sitting height of the driver.
In the method suggested in Patent document No. 1 that adjusts the angle of a mirror that projects an image onto a combiner, the angle of a beam of light that is incident on the combiner is changed for the adjustment. Therefore, if the angle of a beam of light that is changed is large, an image that is recognized as a virtual image on the combiner may become distorted. Also, in a device suggested in Patent document No. 2, it can be expected that an increase in the size of the device for the adjustment of an angle causes a problem that the adjustment cannot be appropriately made in a vehicle with a limited space for installation or that the device cannot be installed in the first place.